Auto-ignition method



AUTO-IGNITION METHOD William P. Webb, San Rafael, Calif., assignor to California Research Corporation, San Francisco, Caliii, a corporation of Delaware No Drawing. Application April 9, 1954 Serial No. 422,257

6 Claims. (Cl. 60-354) many years found use in the construction of asserted tools of war for use against personnel and property. More recently it has been recognized that self-igniting compositions are useful as propellants for rockets, guided missiles and aircraft powered by jet or thrust engines.

Further, self-igniting compositions are useful in initiating combustion in areas in which the usual methods of initiating combustion can be employed only with great difiiculty and inconvenience if at all. For example, selfigniting compositions may be employed to initiate combustion in depleted oil-bearing formations to effect secondary recovery of residual oil in the formation by burning a part of the residual oil and recovering any substantial portion of the remaining residual oil by evaporation, cracking and gas drive of the combustion gases at a producing well.

Hypergolic fuels are useful in the operation of thrust engines. Hypergolic fuels may be generally described as mixtures of a reducing component and an oxidizing component. The individual components of the hypergolic fuel are not self-igniting, but when the two components are mixed there is a short period during which relatively slow reaction of the two components apparently occurs, and this relatively slow reaction is followed by spontaneous ignition of the mixture. Practically all practical hypergolic mixtures have short ignition delay periods substantially less than 1 second and preferably not more than about 50 milliseconds. The reducing component of a hypergolic fuel should have certain properties, as follows: It should ignite spontaneously upon being combined with the selected oxidizing agent; the ignition delay period should be short, preferably not exceeding 50 milliseconds; it should have a low freezing point so that it can be pumped to the combustion chamber at the low temperatures prevailing at high altitudes; it should have a high boiling point to facilitate handling and increase its safety in use; it should be chemically stable in storage; it should have a relatively low viscosity at low temperatures; it should form gaseous oxidation products and the average molecular weight of these products should be as low as possible in order that the specific impulse (pounds thrust/ pounds propellant/second) be high. In addition to the foregoing properties, it is desirable that self-ignition of the mixture of the reducing component and the oxidizing agent be rapid over a wide temperature range; that the reducing component have a high density so that the volume of fuel tanks may be reduced; that the material be nontoxic and easy to handle; that it have a high heat of combustion; and that it be non-corrosive.

-It has now been found that a fire can be started by rapid auto-ignition by mixing a Mannich reaction product of an aldehyde containing 1-7 carbon atoms per molecule, a mercaptan containing 1-4 carbon atoms per molecule and a material of the group consisting of ammonia, low molecular weight primary amines and low molecular weight secondary amines with fuming nitric acids, hydrogen peroxide or N 0 Low. molecular weight amines as,

herein used denotes amines having molecular 'weights below about 125.

The Mannich reaction is a condensation well known in the art. Pursuant to that reaction, ammonia or a lowmolecular weight amine is condensed with an aldehyde and a mercaptan according to the following equations:

--R and R are alkylgroups or may be the cycloalkyl p01:

tion of a heterocyclic amine such as piperidine or morpholine. R is hydrogen, a lower alkyl group, a lower aryl group such as" the benzyl or phenyl group, or a heterocyclic radical such as the furfuryl radical. R' is a lower alkyl group. The products of the above reactions may be characterized as amino sulfides and correspond to the general formula:

in which the Rs are organic radicals and n is any number from 0 to 2.; A number of amino sulfides were prepared by the Mannich reaction and these materials were tested for self-ignition by a simpledrop test. lnthis test the Mannich reaction products were dropped from a capillary pipette into a pool of concentrated (100%) nitric acid contained in the bottom of a Pyrex tube. As standard quantities, 0.13 cc. of the Mannich reaction product and 0.40 cc. of nitric acid are used. Spontaneous ignition is indicated by a flash of light in the bottom of the Pyrex tube. Occasionally, when testing a fuel and it is found that ignition does not occur, activity of the fuel may be indicated by evolution of fumes and heat from the mixture. The drop tests were conducted at room temperature.

-All of the Mannich reaction products listed in Table l 'it is desirable that the hypergolic mixtures have short ignition delay periods, i. e., it is desirable that the time elapsing between the mixing of the two components and the occurrence of spontaneous ignition be less than 50 milliseconds. Phrther, it is desirable that this short ignition delayperiod be obtained at low temperatures, for

example, -40 to -70 F., since temperatures in this range are commonly encountered in high altitude operation of aircraft powered by thrust engines. The last column of Table I shows ignition delay periods for a number of Mannichreaction products at low-temperature. The ignition delay period is measured by mixing the Mannich reaction product with the oxidizer (in these tests the oxidizer was a low-freezing, white fuming nitric acid consisting of 92% by weight HNO 4% by weight NaNO and 4% H O) in a specially constructed cylinder so arranged that at the instant of mixing the Mannich reac- Patented Feb. 18, 1958 l-SR 211 0 Physical properties of dimethylaminodimethyl sulfide are set out in the following Table II:

It will be noted that this compound has physical properties highly desirable in the organic reducing component of a hypergolic mixture intended for use in a thrust engine.

Ignition delays of dimethylaminodimethyl sulfide at various temperatures using red fuming nitric acid (78 by weight HNO;,, 2% by weight H and by weight nitrogen tetraoxide) are shown in the following Table III:

v s Iii-Continued Compound N0. Structural Formula Prepare? From y B. P., o. M.1 .,1F. IgMDeL v p Am ine Mer captan Carbonyl S.)

26'77-24-2 blethylemlnomethylthloaeetete; jie'th lnu. w ne n aide- "7 mm CHsC 2 O N-oHr-S--CH:

CHaCH;

77- 8 4,5-Di-(diethylamino)-3,6-dithlaoctane do Ethyl. Glyoxel l I CHgCHg I :1 i v I V v I N-cH-s-cHmm CHICK; CHICK CECIL-S HN V cflsb s 2148-14 3,4-Di-(dimethylamino) 2,5d1thiahexane Dlmethy1-. Methy fin OH, Temp.

I N-cH-s-cm C a V CHI CHa-S-CH- 2223-16-b Diethanolamlnodtmethylsultlde Dlethanol--- Fg r r r gi e- 4 HO--CH:CH:

N-OH -S-CHI J1O-CH2Gs 2223-17B- Di-(methylthiomethyl)ethanolarnlne Wh m M 60-807 29%? I CHr-SCH! HOCH:CH:N

CHg-S-CH; 2148-43-A Di-(niethylthlomethyl)-methylarnine. Methyl fin dn -88/8- 33 Eg CHz-S-OHI CHr-N CHa-S-CHI 1. Melting-po'tnts'wer'e taken on crude distillation product. TABLE -III From the table it will be noted that extremely short Average ignition delay periods are achieved with a number of the Temperature, F. Ig tio Mannich reaction products listed, dimethylaminodimethyl Delay (MS') sulfide, diethylaminomethylethyl sulfide, di-(ethylthio methyl)-ethyl "amine, and 'tri-(ethylthiomethylj-amine {232- being outstanding with respect to the shortness of the 23 ignition delay period. 52

It has been found further that blends of the Mannich reaction products, especially the lower molecular weight Man'nich reaction products with low molecular weight -re'd fuming nitric acidas theoxidizer a're-shown'inthe following Table IV:

TABLE IV Vol. Corrected Vol. Percent Dimethylaminodimethyl Sulfide Percent Average 2 lhiapro- Delay panol (MS.) K

It will be noted that the above blends contain 20 to 40 volume percent of Z-thiapropanol and are markedly superior to either of the individual components in respect to their ignition delay properties.

As indicated above, the Mannich relation products of this invention form hypergolic mixtures with concentrated nitric acid. Commercial nitric acid having a purity in the range from 95 to 100% HNO by weight is a satisfactory oxidizing agent. White fuming nitric acid composed of 98.5% by weight HNO and 1.5% by weight of water is an eifective oxidizing agent. Minor proportions of ignition accelerators or freeze point depressants may be added to the nitric acid which is mixed with the Mannich reaction products to cause spontaneous ignition of the mixture. For example, 2 to 20% by weight of nitrogen dioxide may be dissolved in the nitric acid. This mixture is sometimes referred to as red fuming nitric acid. 2 to 20% by weight sulfuric acid may be added to the nitric acid to accelerate ignition. 2 to 20% of nitrosyl sulfuric acid may be added to the nitric acid as an ignition accelerator. 5 to 25% by weight of a lower alkane sulfonic acid such as methane sulfonic acid, ethane sulfonic acid, and the like, may be added to the nitric acid to produce a mixture characterized by a much reduced freeze point and good ignition properties when mixed with the Mannich reaction products. Nitric acid containing a small amount up to about 4% by weight of sodium nitrite and a small amount up to about 4% by Weight of water has a low freeze point and forms hypergolic mixtures with the Mannich reaction products of the invention.

Many low molecular weight Mannich products (molecular weight less than 220) are hypergolic with 90% hydrogen peroxide. All low molecular weight compounds are hypergolic with liquid nitrogen dioxide (N 0 These two oxidizers, hydrogen peroxide and nitrogen dioxide, are alternate oxidizers, sometimes advocated for use in hypergolic systems.

If the mixtures of nitric acid and Mannich reaction products are to be employed as a thrust engine fuel, it is desirable that the mixture contain approximately the quantity of nitric acid stoichiometrically required for complete oxidation of the organic material to water, carbon dioxide and sulfur dioxide. Maximum thrust appears to be obtained if the nitric acid is present in the mixture at about 85 to 95% of the amount stoichiometrically required for complete oxidation. Where it is sim- 1. The method of starting a fire by auto-ignition, which comprises mixing an organic compound having the formula:

wherein R is a material selected from the group consisting of alkyl and alkenyl radicals containing 1 to 3 carbon atoms, R and R are materials selected from the group consisting of hydrogen and methyl radicals, R is a material selected from the group consisting of alkyl and alkenyl radicals containing 1 to 4 carbon atoms, and n is a number from 0 to 2 inclusive, with fuming nitric acid, the weight ratio of said organic compound to turning nitric acid being in the range 1:5 to 5:1.

2. The method as defined in claim 1, wherein the Mannich reaction product is dimethylaminodimethyl sulfide.

3. The method as defined in claim 1, wherein the Mannich reaction product is dimethylaminomethyl ethyl sulfide.

4. The method as defined in claim 1, wherein the Mannich reaction product is di-(rnethylthiomethyl)-methylamine.

5. The method as defined in claim 1, wherein the Mannich reaction product is tri-(ethylthiomethyl)-amine.

6. The method of starting a fire by auto-ignition which comprises adding fuming nitric acid to a mixture containing about 20 to 40% by volume of a lower thiaalka- 1101 and about to by volume of dimethylaminodimethyl sulfide.

References Cited in the file of this patent UNITED STATES PATENTS 2,282,710 Dietrich May 12, 1942 FOREIGN PATENTS 497,939 Great Britain Dec. 28, 1938 

1. THE METHOD OF STARTIG A FIRE BY AUTO-IGNITION, WHICH COMPRISES MIXING AN ORGANIC COMPOUND HAVING THE FORMULA: 